Can I increase the number of solar panels in the future and connect it into the battery or do I have to get a new battery?

Can I increase the number of solar panels in the future and connect it into the battery or do I have to get a new battery?

Any increase in the number of panels depends on:
Whether the same panels are still available as they need to match the existing panels. This may mean the inverter needs to be replaced, discuss with your solar installer
Whether you have an existing battery, in which case you probably don’t need to replace it but discuss with your solar installer